It's just not my week. Sorry about that.
I can't see anywhere in the source or the upstream web site that indicates which version of the GPL applies. DESCRIPTION and the upstream web site just say "GPL". The source code has no license information at all. According to the GPL, this means we can choose any version, so "License: GPL+" is the proper thing to use, unless you can get clarification from upstream (which you should try to do).
I don't think a dependency on "R >= R-2.8" does anything useful. A proper versioned dependency would be "R >= 2.8". No supported Fedora version shipped with anything older than 2.8, but I'm not sure what might have been in some ancient version of EPEL so I suppose a versioned dependency could be necessary.
* source files match upstream. sha256sum:
dfd2ef9e23e201f2f7e4073c57701092e7b6d25960c38802d6f0527b20765898
plyr_0.1.9.tar.gz
* package meets naming and versioning guidelines.
* specfile is properly named, is cleanly written and uses macros consistently.
* summary is OK.
* description is OK.
* dist tag is present.
* build root is OK.
? license field matches the actual license.
* license is open source-compatible.
* license text not included upstream.
* latest version is being packaged.
* BuildRequires are proper.
* %clean is present.
* package builds in mock (rawhide, x86_64).
* package installs properly.
* rpmlint has acceptable complaints.
? final provides and requires are sane:
R-plyr = 0.1.9-2.fc12
=
/bin/sh
R
? R >= R-2.8
R-RUnit
R-abind
R-tcltk
* %check is necessarily disabled.
* owns the directories it creates.
* doesn't own any directories it shouldn't.
* no duplicates in %files.
* file permissions are appropriate.
* no generically named files
* scriptlets are OK (R module registration).
* code, not content.
* documentation is small, so no -doc subpackage is necessary.
* %docs are not necessary for the proper functioning of the package.

OK, I've finally found some more time to finish this up.
You still have the unnecessary versioned dependency on R, but it's not a blocker so if you really want it, you can keep it.
It's good that you contacted the author, but neither the source nor the upstream web site, nor anything publicly accessible as far as I can tell has any information that verifies that the license is actually GPLv2. What you need to do in this case is include the actual email you received from the author (assuming you did this via email) in the package so that we have some evidence of the actual license. Just include the text of the email as Source1: and install it as %doc.
Now, I've taken long enough with this review and I really don't want to introduce any additional delay into the process, so I'll go ahead and approve this and trust that you'll fix things up before you check the package in.
APPROVED

Wow. Six months later I notice that the fedora-cvs flag was never raised, so of course CVS was never done. If you still want this package to make it into the distribution, please submit a new CVS request (no F-11 any longer, but now we have F-13) and set the fedora-cvs flag to '?'. Otherwise I'll close this out.